vmsig: management daemon, runtime endpoint lifecycle, roster, discovery, in-tree drivers, packaging

- core: runtime attach/detach of a per-endpoint adapter trio (runtime-safe add_adapter + vmsig_core_detach_endpoint, deferred reap)
- roster: VMSIG_EV_ROSTER + CAP_ROSTER, retained per-endpoint and replayed to late subscribers
- discovery: inotify trigger dir, vmid/endpoint slot allocator, host probe; vmsigd daemon with config + per-uid admission
- input driver and vgpu perception built in-tree; vgpu perception as a separate library
- memctx: own the supplied ro_fd (closed at detach)
- deb packaging: install rules, systemd unit, tmpfiles, default config

packaging/config/vmsigd.conf

@@ -0,0 +1,27 @@
+# vmsigd.conf — vmsig management daemon configuration.
+# Installed as a dpkg conffile (operator edits are preserved across upgrades).
+
+# Control listener the consumer dials. '@' prefix => abstract namespace.
+socket   = /run/vmsig/vmsigd.sock
+
+# Discovery namespace: a VM is managed iff its guest-RAM backing file appears here as
+# vm-<vmid>-ram. The daemon owns this directory (created at boot via tmpfiles).
+watch    = /dev/shm/vmsig
+
+# Inventory source of truth (read on demand; not watched) and the QMP socket directory.
+pve_conf = /etc/pve/qemu-server
+qmp_dir  = /var/run/qemu-server
+
+# vmid<->endpoint slot persistence (tmpfs; re-derived per daemon restart). "" => off.
+slots    = /dev/shm/vmsig/.slots
+
+# ---- Admission policy: one [grant uid=N] stanza per local uid. -----------------------
+# Entitlements are COARSE (the control enforces per-user caps behind the grant). `vmids`
+# is either `*` (all VMs) or a list of vmids; it is translated to endpoint bits at connect
+# time. `caps` is a comma list of: observe,input,lifecycle,power,vm,memctx,memwrite,roster.
+#
+# Example (edit before enabling the service):
+# [grant uid=0]
+# vmids    = *
+# caps     = observe,input,lifecycle,power,vm,memctx,memwrite,roster
+# arb_prio = 100